Apparatus for removing minerals from ore

ABSTRACT

An apparatus for electrolytically precipitating copper dissolved from ores and the like wherein the precipitation is accomplished with a pulsating direct current. The direct current supplied to the anode and cathode is periodically reversed in polarity with respect to the anode and cathode whereby the previous anode becomes the cathode and the previous cathode becomes the anode. Upon reversal of the polarity, the copper precipitated on the previous cathode falls off of the then functioning anode. There is also provided an improved electrolyte for use in the process containing sulfuric acid with a minor amount of lead dissolved therein.

United States Patent 91 Brown et al.

APPARATUS FOR REMOVING MINERALS FROM ORE Inventors: Donald A. Brown, Lakeside; George W. Leech, Whiteriver, both of Ariz.

Assignee: Bro-Lee Incorporated, Globe, Ariz.

Filed: April 21, 1970 Appl. No.: 30,502

Related U.S. Application Data Continuation-impart of Ser. No. 670,595, Sept. 26, 1967, Pat. No. 3,535,218.

U.S. Cl ..204/228, 204/DIG. 8, 204/DIG. 9 Int. Cl. ..B0lk 3/00 Field of Search.....204/D1G. 8, DIG. 9, 228, 106

References Cited UNITED STATES PATENTS 1,956,4l1 4/1934 Bonine ..204/228 X 3,294,666 12/1966 Wiersma ..204/228 3,192,146 6/1965 Vellas et al. ..204/276 X 3,560,263 2/1971 Swinkels ..204/228 X Primary Examiner-John H. Mack Assistant Examiner-D. R. Valentine AttorneyCushman, Darby & Cushman {57] ABSTRACT An apparatus for electrolytically precipitating copper dissolved from ores and the like wherein the precipitation is accomplished with a pulsating direct current. The direct current supplied to the anode and cathode is periodically reversed in polarity with respect to the anode and cathode whereby the previous anode becomes the cathode and the previous cathode becomes the anode. Upon reversal of the polarity, the copper precipitated on the previous cathode falls off of the then functioning anode. There is also provided an improved electrolyte for use in the process containing sulfuric acid with a minor amount of lead dissolved therein.

1 1 Claims, 5 Drawing Figures APPARATUS FOR REMOVING MINERALS FROM ORE This is a continuation-in-part of co-pending application Ser. No. 670,595, filed Sept. 26, 1967, now U.S. Pat. No. 3,535,218.

This invention relates to an apparatus for electrowinning and electrorefining of copper, and more particularly relates to the electrolysis operation of such apparatus for use therein.

It is well known that copper may be recovered from ores or crude copper by electrolytic precipitation. While the particular details of the various processes in use today vary depending on the quality and type of ore or crude copper as well as economical plant construction and power cost, the central step of such processes is the electrolytic precipitation of the dissolved copper Since the present invention relates particularly to this central step, all of the variations and particular details of the many processes for which the present invention is applicable, will not be described in detail but described and explained in relation to the more common processes. However, it is to be understood that the invention may be practiced with any of the electrowinning or electrorefining processes. Even more particularly, the invention will be described in connection with electrowinning processes, but it will be readily apparent that the invention is equally applicable to electrorefining processes.

In electrowinning processes the copper ore is leached in large tanl ts which are generally made of concrete and which may be optionally lined with mastic, lead, plastic and other acid resistant materials. However, wooden, glass and acid resistant metal tanks may be used. The leaching liquid is generally sulfuric acid which may optionally contain minor amounts of additive such as glue and other viscosity controlling agents, as well as ingredients useful with particular ores. For example, iron may be added to the sulfuric acid to form a l-l SO,,FE (SO,,) solution and is particularly useful with mixed oxide and sulfide copper ores. Often the iron is obtained from detinned tin-plate scrap such as conventional tin" cans. The leaching operation may be carried out in one or more steps and may be preceded by a water washing to first remove water soluble minerals. The leaching step may be a batch operation with a definite soaking period or continuous with the leaching liquor being moved through a bed of ore. However, for purposes of this invention, the leaching may be carried out as desired, since the only necessary consideration is that of dissolving as much copper as possible in the most economical way. The leaching liquid, pregnant with dissolved copper, is generally filtered, decanted or otherwise processed to remove a substantial portion of insolubles, such as mud. Commonly, the pregnant liquor is dechloridized by means well known in the art, after the removal of insolubles. While other treatments of the ore and liquor may be performed, depending on the particular ore and process, such as crushing and roasting the ore, concentrating the liquor, etc. the liquor from which the insolubles have been removed is substantially in condition of electrolysis.

The electrolytic precipitation step is quite similar, whether performed as an electrowinning process or an electrorefining process, the major difference being that soluble anodes are normally used in the latter process.

In the electrowinning process the insoluble anodes are normally made of alloys of copper, silicon, iron and lead with small amounts of tin and other metals. However, other anodes such as antimony-lead anodes are also commonly used. The pregnant leach liquor is passed into tanks, referred to as cells, which may be similar in construction to the leach tanks. A DC. current with a voltage of l to 5 volts between the cathode and anode is supplied. The copper is precipitated on the cathode in relatively pure form. The temperature of the electrolytic cells is normally maintained between 20 and 50C and the current density of the electrodes is normally maintained between 10 and 40 amps/sq. ft.

While the above described processes are explained in general as background information, the more particular details are well known in the art. See Mantell, Industrial Electrochemistry, McGraw-I-lill Book Co., N.Y., N.Y., 3d ED., pages 268-293 and 333-347, and U.S. Pat. No. 3,262,870, which disclosures are hereby incorporated by reference.

The known electrolytic precipitation processes and apparatus suffer, however, from common disadvantages. Most notably, the copper precipitated on the cathode is more or less tightly adhered thereto, and periodically the process must be discontinued and the cathodes scraped and/or replaced. This results in an uneconomical use of the process equipment and requires many valuable man-hours of labor. While many attempts have been made in the art to eliminate this problem, such as coating the cathodes with various coatings and release agents, none have been satisfactory and in addition, tend to place unwanted impurities in the copper. Furthermore, as the amount of copper adhering to the cathode increases, the efficiency of the electrolytic cell decreases and results in greater cost of operation. There is, therefore, a long-felt need in the art for an apparatus in which the electrolytic precipitation of copper may be carried out in a continuous manner and without the necessity of frequent interruption of the process.

It is therefore an object of this invention to provide an apparatus that may be continuously operated, which will maintain high cell efficiency and eliminate the wasteful process stoppage and cathode scraping and/or replacement. Other objects will be apparent from the following disclosure and claims.

Briefly stated, the present invention provides an apparatus for electrolytic precipitation of copper wherein the precipitating current is a pulsating direct current and the electrodes previously functioning as the cathode and anode are periodically caused to function as the opposite electrode, i.e., the cathode becomes the anode and the anode becomes the cathode. As a result of the pulsating direct current very pure copper precipitates on the cathode, and upon reversing the cathode to become the anode, the precipitated copper drops off of the previous cathode (now the anode) while additional copper is being precipitated on the previous anode (now the cathode).

While many conducting materials may be used as the electrodes of this process with some degree of success, it has been found that electrodes constructed of nonmagnetic materials provide better results and are less subject to deterioration. In particular, stainless steel type materials give far better results than any other materials.

For purposes of this invention stainless steel type material is meant to encompass those alloys having major proportions of iron and chromium and iron, chromium and nickel. The percent of chromium may be as low as 3 percent or lower or as high as 30 percent or greater. Preferably, the stainless steel should contain at least 12 percent chromium and more preferably about 18 percent chromium or greater. The nickel content may be as low as 2 percent, but at least 6 or 7 percent is preferred. Other minor amounts of components may be included in the stainless steel type material contemplated, such as molybdenum and silicon. Examples of suitable stainless steel type materials are 301, 304, 316, 403 and 416 stainless steel. In general, the optimum stainless steel type material will depend on the oxygen and hydrogen content of the pregnant leach liquor, as well as the concentration of sulfuric acid therein and temperatures of liquor. A suitable material may easily be chosen by simple standard corrosion test using the contemplated pregnant leach liquor. However, for most applications, it has been found that 316 stainless steel is the preferred material.

The voltage and current density used in accordance with this invention is not critical, but generally the voltage will be between 1 and 6 volts and the current density will be between 10 and 60 amps/sq. ft. A preferred set of conditions is that of about 2.75 to 4.5 volts and about 20-40 amps/sq. ft. current density.

The concentration of sulfuric acid and dissolved copper in the leach liquor is also not critical and may vary widely. The sulfuric acid content may be as low as grams per liter or lower up to as high as 400 grams per liter or greater. The dissolved copper content of the leach liquor may be from as low as grams per liter or lower up to any concentration economically feasible. Representative amounts of dissolved copper will be between 25-70 grams per liter of leach liquor.

The temperature of the pregnant leach liquor in the electrolytic precipitation step may range widely and from l090C would be suitable. However, a temperature of about 20-50C is preferred and about 40C is an excellent operating temperature.

Turning now to the drawings wherein:

FIG. 1 is a diagrammatic illustration of a suitable electrolytic cell;

FIG. 2 is a diagram of a suitable circuit according to the present invention;

FIG. 3 is an alternate circuit; and

FIG. 4 shows another circuit arrangement according to this invention; and

FIG. 5 is an overall schematic plan of an illustrated process using the present invention.

Referring to FIG. I, there is shown a cell tank 1 illustrated as a concrete tank, which may have a protective inside surface 2. Disposed in the cell are anode plates 3 and cathode plates 4, supported by the anode bus bars 5 and cathode bus bar 6. The plates may be supported by the bus bar in any conventional fashion such as by bolting, clamping, slots and studs. The only necessary considerations are those of rigidity and good electrical contact.

The anode and cathode plates may be any desired size of configuration, but a rectangular shape is most convenient. The plates are disposed above the bottom of the cell 7, so that there is some clearance therebetween, preferably several inches or more. The

space between the plates is not critical, but from I to S inches is especially suitable. The bus bars have suitable terminal lugs 8 and 9 for attaching electrical cables thereto. Of course, any suitable device for attaching the electrical cables may be used. In operation, the pregnant liquor is pumped into the cell by any suitable means (now shown) such as pipes and hoses either above, in or under the tank. The pregnant liquor may be pumped into and out of the tank batchwise or pumped continuously in and out of the tank to provide a continuous operation. The copper which drops to the bottom of the tank also may be removed batchwise by flushing through a drain (not shown) or scooped or otherwise, or may be continuously removed by a travel.- ing belt, scoops or continuously drained out by a bottom drain or otherwise.

The temperature of the pregnant liquor may be maintained by heating the incoming liquor, the tank or both. Other means of heating will be readily apparent to one skilled in the art.

In FIG. 2, there is shown a suitable method according to this invention of obtaining a pulsating direct current signal by which is meant a train of pulses, such as half wave rectified signals, with a direct current component. In this embodiment, alternating current generated by any conventional generating machinery and of any desired voltage and cycles per second is supplied to a conventional step-down transformer, generally designated as 10, having a primary coil 11, and a secondary coil 12. If the voltage generated is chosen in connection with the particular step-down transformer any desired voltage may be obtained in the secondary coil 12. Of course, rheostats and like devices may also be used to control the voltage, if desired. One side of the step-down transformer is connected in parallel with a pair of diodes 13 and 14 or like rectifying devices which allow current to pass in opposite directions whereby pulsating direct current of opposite polarity is directed to the anode l5 and cathode 16. In FIG. 2, diode 14 is illustrated as a positive current passing diode while diode 13 is illustrated as a negative current passing diode. The other side of the step-down transformer is connected to the opposite electrodes 17 and 18. While the process of this invention may be operated with only one diode, or a number of diodes all of which are hooked in parallel, this arrangement utilizes only either the positive or negative excursions of the alternating current sine wave, and it is more advantageous to use an arrangement as illustrated in FIG. 2 where at least one pair of diodes are provided and wherein the two diodes pass opposite polarity current, so as to utilize the entire alternating current wave form. Furthermore, a series of cells may be hooked onto the electrical cables carrying the pulsating direct current, providing a bank of cells in parallel.

In practice, a switching device, many of which are known to the art, is attached at any convenient place in the circuit to reverse the polarity of the plates in the cell. For example, such a device could be placed just after the diodes 13 and 14; if preferred, the cables connecting the diodes and plates can be manually reversed by hand. However, in practice, a timer is placed in the circuit in conjunction with the switching device whereby the length of time that one set of plates functions as the cathode and then alternately as the anode may be controlled. Many such timing devices are known to the art.

One suitable and simple arrangement for automatically reversing the cathode and anode plates at periodic intervals is illustrated in FIG. 3. In this arrangement, a conventional source of alternating current, for example l volts at 60 cycles per second, is applied to the primary windings of a conventional, step-down transformer 22 via on-off switches 24 and 26 and normally open switches 28 and 30.

When the operation of the system is initiated by the closing of switches 24 and 26, a current path is completed through coil 32 of timer 34 which thereafter begins marking time. The passage of current through coil 32 also closes controlled switch 36 completing a current path through coil 38.

Also at this time, one of the switches 40 or 42 in timer 34 will be open and the other closed. Assuming switch 40 is closed, a current path is completed through coil 44 of relay 46 which responds by closing its controlled, normally open switches 48 and 50. The closing of these two switches completes a current path between the anode an cathode plates indicated as P-land P-2 via secondary winding 52, diodes 54, 56 and 58, switch 48 and switch 50. The system then proceeds to remove the copper and other material from the bath as indicated above as the pulsating, half-rectified signal is applied between the plates.

After the time preset in timer 34 has elapsed, timer 34 opens switch 36, interrupting the flow of current through coil 38 which permits its normally controlled switches 28 and 30 to return to their illustrated positions. The opening of switches 28 and 30 interrupts the flow of current through primary winding 20, which also interrupts the flow of current through switches 48 and 50 so that they can be opened without any danger of arcing. After switch 36 has been opened, switch 40 is now opened and switch 42 is closed. Finally switch 36 is reclosed, permitting current to flow once more through coil 38 which then closes switches 28 and 30 so that the current path through primary winding 20 is recompleted.

The closing of switch 42 completes a current path through coil 54 which then closes normally open switches 56 and 58. These switches connect the plates P-1 and P-2 to secondary winding 52 oppositely to the way in which they were connected to secondary winding 52 by switches 48 and 50 so that the previous cathode plates becomes anode plates and the previous anode plates cathode plates. Timer 34 now begins timing a new cycle and when the preset time has elapsed switch 36 is opened, switch 40 reclosed, switch 42 reopened, and then switch 36 reclosed. This cyclical operation continues until on-off switches 24 and 26 are opened.

Reference-is now made to FIG. 4 which shows a circuit, similar to the one illustrated in FIG. 2, for applying a pulsating, direct current signal to the plates. As in FIG. 2, a source of alternating current voltage, e.g., 220 volts at 60 c/s, is applied across the primary winding 60 of a conventional transformer 62. A switch 64 is provided so that the source can be connected either to the end of winding 60 or to any of three taps as shown in order to control the current induced in the secondary windings of transformer 62.

However, the embodiment illustrated in FIG. 4 differs from the embodiment of FIG. 2 in that transformer 62 has two secondary windings 66 and 68, each with an appropriate number of turns so that appropriate currents are induced in each. Thus each of the secondary windings 66 and 68 carries only half the current that the secondary winding in FIG. 2 must carry if the currents through the plates in each of the Figures is to be the same. This may improve considerably the current carrying ability of the system.

Further in this embodiment the current to each set of plates is fed through a separate diode rather than through a common diode as in FIG. 2. Diodes 70, 72, 74, 76 and 78 each generate a half wave rectified signal which is applied to a pair of plates and diodes 80, 82, 84, 86 and 88 each generate half wave rectified signals of opposite polarity which are applied to similar pairs of plates. The currents I and I which flow through secondary windings 66 and 68 are also shown in FIG. 4.

It will of course be appreciated that while each tank is shown with five pairs of plates, normally each tank will have many more and in fact as many as possible in accordance with the maximum current carrying ability of transformer 62. Further each pair of plates in the embodiment of FIG. 4 is preferably equipped with its own diode or diodes which therefore need carry only the current to that pair of plates.

While diodes are preferred as the current rectifying elements in the embodiments of FIGS. 2 and 4, it will of course be appreciated that any suitable arrangement for generating a pulsating signal with a direct current component can be alternately employed. For example, a full wave rectifying bridge of four diodes could be used instead of the single diode half wave rectifiers of FIGS. 2 and 4. If diodes are to be employed, any conventional type such as a rectifier tube, a selenium rectifier or an SCR can be used.

Referring to FIG. 5, the overall process is shown. In Step 1 the ore is prepared according to the particular leaching process contemplated and according to the ore to be used; the ore is then leached in Step 2 and the pregnant leach liquor is sent to the electrolytic cell, Step 3, where the copper is precipitated and the leach liquor sent to a holding vessel, Step 4. The leach liquor from the holding vessel may be recirculated again through the electrolytic cell for further removal of copper or sent to the leaching step for dissolving further copper from fresh ore or for further dissolving copper from the already leached ore. Of course, a combination of the above may be accomplished if desired. The copper removed from Step 3 is washed and dried, if desired, and packaged for market.

The frequency of the pulsating direct current may vary over a wide range, from as low as about 600 pulses per minute or lower to as high as about 3 million pulses per minute or higher. The preferred range, however, is between 3,000 and 4,200 pulses per minute.

According to a further feature of the present invention, it has been found that the efficiency of the electrolytic precipitation and ease of the precipitated copper falling from the electrode plate upon reversing the current is improved if a minor amount of lead is dissolved in the pregnant leach liquor. Conveniently the lead is dissolved in the leach liquor in the form of a salt; an especially convenient form is that of lead sulfate.

Example 1 A copper ore consisting of mixed oxides and sulfides in which the total copper of the ore was about 1.2 percent by weight was crushed and washed. The ore was transferred into a cement leaching tank wherein leaching liquor, containing 125 g/l of sulfuric acid and about 6 g/l of ferric sulfate, was percolated up through the ore at a rate whereby the leaching liquor contained about 35 g/l of dissolved copper when it reached the top of the leaching tank. The pregnant liquor was drawn off the top of the tank and continuously flowed into a settling tank where the suspended insolubles were allowed to settle as the pregnant liquor slowly flowed through the tank. The pregnant liquor was then filtered to further remove suspended solids. After filtering, the pregnant liquid was heated to about 40C and flowed into an electrolytic precipitating cell as shown in FIG. 1 with 316 stainless steel electrodes. A pulsating direct current was supplied to the cell at 2.75 volts and at a current density of 30 amp/sq. ft. with 3,600 pulses per minute. The pregnant liquor was continually recirculated out of and back into the cell. After two hours of operation, the cathode had a thick coating of copper adhered thereto. The polarity of the electrodes was reversed and copper began to precipitate on the previous anode (now a cathode) and the copper deposited on the previous cathode (now an anode) began to fall off. After a further 2 hours of operation the previous cathode (now the anode) was almost completely clean with only very minor amounts of copper remaining adhered to the plate. The copper which had fallen to the bottom of the cell was removed and various samples were analyzed. The sample averaged at least 97 percent pure copper.

Example 2 The procedure of Example 1 was repeated on a different sample of ore known to be contaminated with many minerals. The polarity of the electrodes was reversed every 1 /2 hours in a continuous operation for 30 days. Periodically, the copper which had fallen to the bottom of the cell was removed and fresh pregnant liquor was blended'with the liquor being recirculated, while part of the liquor withdrawn from the cell was recycled to the leaching tank. After the 30 days operation the electrodes showed only a slight accumulation of precipitated copper. Many samples were removed from the cell during operation and later combined into one sample with blending. A spectrographic analysis of the combined samples is shown in Table 1. Note that the present invention is capable of recovering a wide variety of elements from mixed ores, which elements may be separated in known ways if desired.

TABLE I Percent by weight N 0t rletected-lcss than 0.008. Not detectedless than 0.04.

. Not detected-less than 0.00006. Not detectedless than 0.002. Nnt detectedless than 0.02.

. Not detectcdlcss than 0.20.

Not detectedless than 0.0005. Not detectedless than 0.02. Not detected-less than 0.004. Not detected-less than 0.003. Nnt detected-Jess than 0.003.

Not detcetedless than 0.05. Not detected-less than 0.02. Not detecterllcss than 0.04.

Mercury Not detectedless than 0.05.

Molybdenum Not detected-less than 0.001.

Platinum Not detected-less than 0.004.

Phosphorus Not detected-dens than 0.03.

Rhenium Not dctectedless than 0.005.

Ruthenium r Not detcctedless than 0.006.

Rubidium Not detertedless than 0.20. Sodinm Not detectcdlcss than 0.04. Tantalum Not detcctcdlcss than 0.10. Tellurium... Not detected-Jess than 0.06. Thal1ium.. Not detcctedlcss than 0.07. Tungsten Not detected-less than 0.04. Vanadium Not deteetcdless than 0.00l. Zinc Not detected-less than 0.002. Zirconnn Not detected-less than 0.003. Rare earths Nil.

Example 3 The procedure of Example 2 was repeated with the ore of Example 1 except that 0.1 percent of lead sulfate was added to the pregnant liquor prior to entry into the electrolytic cell. After 30 days operation, the electrodes had only traces of copper remaining thereon.

Example 4 The procedure of Example 1 was repeated under the conditions shown below and with the noted results.

Current Amount of Copper Test Voltage Density D.C. Remaining on Pulses No.

V. Amps/ft Per Previous Cathode minute 1 1.00 30 2900 Trace 2 I .25 30 3000 Trace 3 [.75 30 3600 None 4 2.50 34 3200 Trace 5 3.50 27 3300 Trace 6 4.25 35 3400 Trace 7 4.75 30 3600 None 8 5.50 31 3800 Trace 9 6.25 30 4200 Trace l0 7.00 28 6000 Slight Example The procedure of Example 4 was repeated except that 1.5 percent lead sulfate was added to the pregnant liquor. In all tests except 9 and no copper remained on the previous cathode. In Tests 9 and 10 trace amounts remained.

Example 6 The procedure of Example 1 was repeated except that the current density was varied from 10 amps/sq. ft. to 60 ampsfsq. ft. in 10 amps/ft. increments. Only trace amounts of copper remained on the previous cathode except at the 50 and 60 amps/sq. ft. test where traces remained and at the 30 amps/sq. ft. test where no copper remained.

Example 7 The procedure of Example 6 was repeated five times except that lead sulfate was added to the pregnant liquor in amounts of 0.1 percent, 1 percent, 3 percent, 5 percent, and 7 percent, respectively in each test. No copper remained on the previous cathode in any of the tests except where the current density was 50 and 60 amps/sq. ft. where only trace or slight trace amounts remained.

From the above examples, it can be seen that the objects of the invention have been accomplished. Also, from the above, it will be apparent to one skilled in the art that the present invention is equally applicable to electrorefining processes. For example, a conventional copper starter sheet may be formed in a conventional way and used as the anode. After the starter sheet has been dissolved and precipitated on the cathode, according to the process of the present invention, a stainless steel type plate may be inserted in the cell and function as a new cathode with the previous cathode, having the refined copper precipitated thereon, functioning as the anode. During the subsequent operation of the process, the refined copper will drop to the bottom of the tank.

As is apparent from the above disclosure, the present invention is applicable to extracting copper from any copper containing material, from which the copper can be electrolytically precipitated, and many variations of the above disclosures will be readily apparent to one skilled in the art. Therefore, the present invention is to include such apparent variations and is limited only by the scope and spirit of the following claims.

What is claimed is 1. An apparatus for electrolytic precipitation of minerals from a copper containing ore comprising:

a tank,

a first and second series of electrodes disposed therein in spaced relationship,

a third and fourth series of electrodes disposed therein in spaced relationship,

the lower edges of the electrodes being disposed above the bottom of the tank,

a first means electrically connecting the first series of electrodes, a second means electrically connecting the second series of electrodes, a third means electrically connecting the third series of electrodes, and a fourth means electrically connecting the fourth series of electrodes, I

means for supplying a pulsating direct current to each of the said first and second means and to each of the said third and fourth means wherein the said first and second means are of opposite polarity and the third and fourth means are of opposite polarity including a voltage step-down transformer having a primary winding adapted for connection to a source of alternating current and a first and second secondary winding, first current rectifying means connecting said electrodes of said first series to one side of said first winding with said electrodes of said second series being connected to the other side of said first winding and second current rectifying means connecting said electrodes of said third series to one side of said second winding with the said electrodes of said fourth series being connected to the other side of said second winding, and

means for periodically reversing the polarity of the said first and second means and of said third and fourth means.

2. The apparatus of claim 1 wherein the said first and second means are bus bars.

3. The apparatus of claim 1 wherein the means for supplying the pulsating direct current comprises a means for providing an alternating current signal and at least one diode connected to one side of the source of alternating current for rectifying said alternating current signal so that said pulsating direct current is produced.

4. The apparatus of claim 1 wherein the electrodes are made of a stainless steel type material.

5. The apparatus of claim 4 wherein the stainless steel type material is 316 stainless steel.

6. The apparatus of claim 1 wherein the means for supplying the pulsating direct current pulsates the current between 600 and 3 million times per minute.

7. The apparatus of claim 6 wherein the said supplying means pulsates the current between 300 and 4,200 times per minute.

8. An apparatus for electrolytic precipitation of copper comprising:

a tank,

at least a first and second electrode disposed therein in spaced relationship at least a third and fourth electrode disposed in said tank in spaced relationship the lower edges of the electrodes being disposed above the bottom of the tank,

means for causing a pulsating current having a direct current component to flow between said first and second electrodes and between said third and fourth electrodes so that said first and second electrodes are of opposite polarity and said third and fourth electrodes are of opposite polarity including a voltage step-down transformer having a primary winding adapted for connection to a source of alternating current and a first and second secondary winding, first current rectifying means connecting said first electrode to one side of said first winding with said second electrode being connected to the other side of said first winding and second current rectifying means connecting said third electrode to one side of said second winding with the said fourth electrode being connected to the other side of said second winding, and

means for periodically reversing the polarity of said first and second electrodes and of said third and fourth electrodes so that current then flows in the opposite direction.

9. The apparatus of claim 8 wherein said first rectify-' ing means is a diode connected to conduct current dur-' ing positive excursions of said alternating current and said second rectifying means is a diode connected to conduct current during negative excursions of said alternating current. 

1. An apparatus for electrolytic precipitation of minerals from a copper containing ore comprising: a tank, a first and second series of electrodes disposed therein in spaced relationship, a third and fourth series of electrodes disposed therein in spaced relationship, the lower edges of the electrodes being disposed above the bottom of the tank, a first means electrically connecting the first series of electrodes, a second means electrically connecting the second series of electrodes, a third means electrically connecting the third series of electrodes, and a fourth means electrically connecting the fourth series of electrodes, means for supplying a pulsating direct current to each of the said first and second means and to each of the said third and fourth means wherein the said first and second means are of opposite polarity and the third and fourth means are of opposite polarity including a voltage step-down transformer having a primary winding adapted for connection to a source of alternating current and a first and second secondary winding, first current rectifying means connecting said electrodes of said first series to one side of said first winding with said electrodes of said second series being connected to the other side of said first winding and second current rectifying means connecting said electrodes of said third series to one side of said second winding with the said electrodes of said fourth series being connected to the other side of said second winding, and means for periodically reversing the polarity of the said first and second means and of said third and fourth means.
 2. The apparatus of claim 1 wherein the said first and second means are bus bars.
 3. The apparatus of claim 1 wherein the means for supplying the pulsating direct current comprises a means for providing an alternating current signal and at least one diode connected to one side of the source of alternating current for rectifying said alternating current signal so that said pulsating direct current is produced.
 4. The apparatus of claim 1 wherein the electrodes are made of a stainless steel type material.
 5. The apparatus of claim 4 wherein the stainless steel type material is 316 stainless steel.
 6. The apparatus of claim 1 wherein the means for supplying the pulsating direct current pulsates the current between 600 and 3 million times per minute.
 7. The apparatus of claim 6 wherein the said supplying means pulsates the current between 300 and 4,200 times per minute.
 8. An apparatus for electrolytic precipitation of copper comprising: a tank, at least a fiRst and second electrode disposed therein in spaced relationship at least a third and fourth electrode disposed in said tank in spaced relationship the lower edges of the electrodes being disposed above the bottom of the tank, means for causing a pulsating current having a direct current component to flow between said first and second electrodes and between said third and fourth electrodes so that said first and second electrodes are of opposite polarity and said third and fourth electrodes are of opposite polarity including a voltage step-down transformer having a primary winding adapted for connection to a source of alternating current and a first and second secondary winding, first current rectifying means connecting said first electrode to one side of said first winding with said second electrode being connected to the other side of said first winding and second current rectifying means connecting said third electrode to one side of said second winding with the said fourth electrode being connected to the other side of said second winding, and means for periodically reversing the polarity of said first and second electrodes and of said third and fourth electrodes so that current then flows in the opposite direction.
 9. The apparatus of claim 8 wherein said first rectifying means is a diode connected to conduct current during positive excursions of said alternating current and said second rectifying means is a diode connected to conduct current during negative excursions of said alternating current.
 10. The apparatus of claim 8 further including a plurality of said first electrodes and a plurality of said second electrodes and wherein said causing means includes a plurality of rectifying means each connecting one of said first electrodes to one side of a source of alternating current with each of said second electrodes being connected to the other side of said source. 